Project Summary. Although exposure to psychosocial stress is a known risk factor for subsequent mental disorders, one of the most vexing problems in psychiatry is the lack of objective markers that can be used to identify individuals who were exposed to stress and are therefore at higher risk of developing neuropsychiatric illnesses. This includes objective markers of exposure to prenatal stress, which is a potent determinant of depression per the ?prenatal programming of mental illness? hypothesis. The currently-funded grant (R01MH113930) is using data primarily from the Avon Longitudinal Study of Parents and Children (ALSPAC) to test the central hypothesis that vulnerability to adolescent- and young adult-onset depression arises, in part, via the effects of adversity-induced DNA methylation (DNAm) changes during an early sensitive period occurring in the first five years of postnatal life. We propose a supplement to enhance our capacity to meet the goals of the parent grant by incorporating two sets of prenatal psychosocial stress measures for use as explanatory variables and covariates in our analyses. These new measures will be derived from maternal self- report and by analyzing children?s shed primary or ?baby? teeth. Since teeth provide a record of their formation process, our working hypothesis is that prenatal stress exposure ? and particularly the timing of exposure ? can be non-invasively measured in shed teeth that formed in utero. In Aim 1, we will validate teeth as a novel and objective measure of prenatal stress exposure. In Aim 2, we will compare the strength of the association between objective tooth-based vs. subjective maternal self-report measures of prenatal psychosocial stress on DNAm signatures at birth. Finally, in Aim 3, we will use a combination of objective tooth-based measures and subjective self-report measures to examine the effects of pre- and postnatal psychosocial stress on DNAm at age 7. If validated as biomarkers, teeth would transform the study of sensitive periods by providing a new, non-invasive measure for capturing and dating prenatal exposures, and would change the standard for how children are screened for prenatal stress exposure and subsequent risk for depression.